The present invention relates to a blue phase (BP) liquid crystal composition and to a method of stabilizing a blue phase state of a liquid crystal material. Furthermore, the present invention relates to a method of lowering the operating voltage of a liquid crystal material. Moreover, the present invention relates to a blue phase liquid crystal material stabilized by the method according to the present invention or having an operating voltage that is lowered by the method according to the present invention. Also, the present invention relates to a liquid crystal cell comprising a blue phase liquid crystal material and to a liquid crystal display comprising a blue phase liquid crystal material. The present invention furthermore relates to a method of broadening the stability temperature range of a liquid crystal material in its blue phase state.
Liquid crystalline blue phases are self-assembled cubic structures which are composed of helically double twisted cylinders. This type of structure is limited to a very narrow temperature range of approximately 1-2° C. To make use of such liquid crystalline blue phases in display applications, the blue phase (BP) must be brought into a state where it is stable over a larger temperature range. In recent years, based on the work of Kikuchi et al., ways have been found to extend the temperature range of blue phase liquid crystals to more than 60° C., wherein the blue phase is stabilized by the help of a polymer network. Coles et al. developed novel bimesogenic materials which yielded temperature ranges of approximately 50° C. over which the blue phase state of a liquid crystal material exists.
A liquid crystalline blue phase is an optically isotropic phase which, upon application of an electric field and based on the Kerr effect, becomes birefringent, and, due to the refractive index distribution of the liquid crystal, turns into an optically anisotropic state which is unlike other liquid crystal phases which are switching from one anisotropic state to another. If the blue phase is brought between two crossed polarizers, the transmittance increases with increase of the voltage. This operation requires application of a considerable voltage as it links up to the induced birefringence which itself is highly dependent on the Kerr constant of the liquid crystal material and also on the strength of the electric field. Although the broadening of the stability temperature range of a blue phase liquid crystal material represents an advancement, there are still drawbacks associated with blue phase liquid crystal materials, such as the high operating voltage which needs to be applied to make the blue phase switch from a dark to a bright state, a relatively low transmittance and the fact that the temperature ranges are still not wide enough for practical applications in displays. Different approaches have been taken to improve the above-mentioned aspects, such as for example by means of an optimization of the electrode structure, a tuning of the liquid crystal and chiral materials, an improvement of the polymer network by using multifunctional monomers (see also reference 1-6).    1. H. Kikuchi, M. Yokota, Y. Hisakado, H. Yang, T. Kajiyama; Nature materials, Vol. 1, 64-68, 2002.    2. H. Coles, M. Pivnenko, Nature, 436, 18, 997-1000, 2005.    3. T. Iwata, K. Suzuki, N. Amaya, H. Higuchi, H. Masunaga, S. Sasaki, H. Kikuchi, Macromolecules, 42, 2002-2008, 2009.    4. Z. Ge, L. Rao, S. Gauza, S.-T. Wu, J. Display Technol., Vol. 5, No. 7, 250-256, 2009    5. H.-S. Kitzerow, Chem Phys Chem 7, 63-66, 2006    6. S. Meiboom, J. P. Sethna, W. P. Anderson, W. F. Brinkman, Phys. Rev. Lett., Vol. 46, 1216-1219, 1981
Current electronic device display technologies require displays with high brightness and contrast, low power consumption and very fast response times for application fields such as three-dimensional displays or field sequential displays. Incorporating liquid crystalline blue phase materials into displays offers the potential to meet several of these requirements, but still the issues of stability of these blue phases and operating voltage of such blue phase liquid crystal materials need to be resolved. Accordingly, it was an object of the present invention to provide for means to increase the stability of blue phase liquid crystal materials. It was also an object of the present invention to provide for means to lower the operating voltage of blue phase liquid crystal materials.